No abstract

Thymic development and somatic growth were investigated in three strains of rat. The well established influence of sex and age on somatic growth was confirmed. It was also found that the rate of thymic growth was not influenced by the sex of the animal until four weeks of age, but thereafter, the thymus grew faster in males compared with females of the same strain. Gonadectomy had a marked effect on the thymus, resulting in a higher rate of growth than in normal animals; but a slower initial rate of involution. The maximum thymus weights attained in gonadectomized animals were found to be independent of the age at which the animals were gonadectomized or of the sex of the animal. Gonadectomy did not influence the point at which involution began. Thymic mitotic indices of gonadectomized animals were found to be higher than those of normal animals. The influence of sex hormones on somatic growth and the development of the thymus is discussed, and it is concluded that cell loss is the regulator of thumus growth and involution.

The purpose ofthis study was to determine the changes in rat gastric functional morphology that take place with age and to study the action of coiloidal bismuth subcitrate on the age related degeneration of the stomach. At 95 weeks of age erosions were apparent over 80% of the gastric mucosa and this was associated with a significant decline in the numbers and mucus content of the mucosal epithelial cells. The rate of stem cell proliferation in the neck region was also significantly lower than that found in 9 week old animals. The administration of 50 mg/kg colloidal bismuth subcitrate for 14 days to 9 week old animals resulted in slight hypertrophy of the mucosal epithelial celis. When 95 week animals were placed on the same regimen there was a decline in the number of deep erosions in the mucosa and an increase in the number and mucin content of the mucosal epithelial cells. A significant increase in the proliferation of the stem cell population was also observed after colloidal bismuth subcitrate administration. It is suggested that coiloidal bismuth subcitrate may ameliorate the increased susceptibility to harmful agents that occurs with age.

The rates of cellular proliferation and cellular death were investigated in the rat thymus during growth and involution. It was found that the percentage of dead cells gradually increased with age, whilst the rate of cell proliferation declined, indicating that a substantial proportion of lymphocytes that divide in the thymus also die there. It was also found that there exists a density-dependent distribution pattern of mitotic and dead cells and that this distribution pattern changed with age. It is suggested that this mechanism of density-dependent control of the thymus may be an important factor in the age involution of the thymus.

The growth of s.c. Walker 256 carcinoma was found to be independent of secondary growths induced by i.v. injection. Tumour cells injected i.v. lodged mainly in the lungs, with small clusters of cells in the lymph nodes. The rate of cellular proliferation of these secondary growths of Walker carcinoma was significantly higher than that observed in the s.c. tumour. In addition, host lung tissue was found to inhibit the development of metastases, and it is postulated that the host tissue may produce a diffusible inhibitor and that differences in the effectiveness of these humoral factors may account, in part, for locational differences in tumour growth patterns.